Computational fluid dynamics analysis of the effect of topographic obstacles on extractable power by horizontal axis wind turbines

Abstract

Wind velocity profile varies in the boundary layer according to a complex pattern that depends hugely on the surface roughness and local Reynolds number. The presence of a macroscopic obstacle on the ground surface modifies considerably the flow characteristics of wind speed profile. In this study, the effect on wind speed resulting from local circulatory motion induced by the existence of an obstacle is analyzed in stationary conditions under the assumption of two-dimensional approximation of the problem. Computational fluid dynamics is used to solve the turbulent air flow equations that consist of Navier–Stokes equations coupled to a K-ε turbulence model. A bounded domain having a rectangular form was introduced in order to schematize the atmospheric region containing the obstacle and wind turbine. The boundary conditions at ground surface were fixed by applying a modified wall law. The other boundary conditions included a logarithmic velocity profile at the input, a uniform speed applied on the upper edge of the rectangular domain and a uniform pressure in the outlet area. To solve the obtained equations, Comsol Multiphysics software package was used. The obtained results have shown that the presence of an obstacle has a huge effect on the wind profile pattern and affects largely the extractable power from wind by the wind turbine system.